Developing Methodology for Elevated Temperature Design of Section VIII, Division 1 Vessels Considering Load Durations Available to Purchase

The rules of Section VIII, Division 1 provide an allowable stress for design of pressure vessels that is independent of load duration. In the time dependent regime, where failure by creep rupture is a consideration, the actual life of the vessel depends on a number of things, including the margins provided in the allowable stresses, the margin between design pressure and operating pressure, the margin between design temperature and operating temperature. While material properties for a time duration of 100,000 hours are included as part of the basis in establishing the allowable stress, this is neither an anticipated life nor a design life for the pressure vessel. There are short term conditions for which design based on an allowable stress set based on long term creep properties is unrealistically conservative. This paper provides recommendations for design rules for very short term loads for which creep should not be a design consideration, termed occasional loads herein, and rules for loads for which creep is a design consideration.